The Poly(ADP-ribose) Polymerase Enzyme Tankyrase Antagonizes Activity of the ß-Catenin Destruction Complex through ADP-ribosylation of Axin and APC2.

Most colon cancer cases are initiated by truncating mutations in the tumor suppressor, adenomatous polyposis coli (APC). APC is a critical negative regulator of the Wnt signaling pathway that participates in a multi-protein "destruction complex" to target the key effector protein ß-catenin for ubiquitin-mediated proteolysis. Prior work has established that the poly(ADP-ribose) polymerase (PARP) enzyme Tankyrase (TNKS) antagonizes destruction complex activity by promoting degradation of the scaffold protein Axin, and recent work suggests that TNKS inhibition is a promising cancer therapy. We performed a yeast two-hybrid (Y2H) screen and uncovered TNKS as a putative binding partner of Drosophila APC2, suggesting that TNKS may play multiple roles in destruction complex regulation. We find that TNKS binds a C-terminal RPQPSG motif in Drosophila APC2, and that this motif is conserved in human APC2, but not human APC1. In addition, we find that APC2 can recruit TNKS into the ß-catenin destruction complex, placing the APC2/TNKS interaction at the correct intracellular location to regulate ß-catenin proteolysis. We further show that TNKS directly PARylates both Drosophila Axin and APC2, but that PARylation does not globally regulate APC2 protein levels as it does for Axin. Moreover, TNKS inhibition in colon cancer cells decreases ß-catenin signaling, which we find cannot be explained solely through Axin stabilization. Instead, our findings suggest that TNKS regulates destruction complex activity at the level of both Axin and APC2, providing further mechanistic insight into TNKS inhibition as a potential Wnt pathway cancer therapy.

Excessive diagnostic testing in acute kidney injury.

BACKGROUND: The patterns, performance characteristics, and yield of diagnostic tests ordered for the evaluation of acute kidney injury (AKI) have not been rigorously evaluated. METHODS: We characterized the frequency of AKI diagnostic testing for urine, blood, radiology, and pathology tests in all adult inpatients who were admitted with or developed AKI (N = 4903 patients with 5731 AKI episodes) during a single calendar year. We assessed the frequency of abnormal test results overall and by AKI stage. We manually reviewed electronic medical records to evaluate the diagnostic yield of selected urine, blood, and radiology tests. Diagnostic yield of urine and blood tests was determined based on whether an abnormal test affected AKI diagnosis or management, whereas diagnostic yield of radiology tests was based on whether an abnormal test resulted in a procedural intervention. In sensitivity analyses we also evaluated appropriateness of testing using prespecified criteria. RESULTS: Frequency of testing increased with higher AKI stage for nearly all diagnostic tests, whereas frequency of detecting an abnormal result increased for some, but not all, tests. Frequency of detecting an abnormal result was highly variable across tests, ranging from 0 % for anti-glomerular basement membrane testing to 71 % for urine protein testing. Many of the tests evaluated had low diagnostic yield. In particular, selected urine and blood tests were unlikely to impact AKI diagnosis or management, whereas radiology tests had greater clinical utility. CONCLUSIONS: In patients with AKI, many of the diagnostic tests performed, even when positive or abnormal, may have limited clinical utility.

Cathelicidin antimicrobial protein, vitamin D, and risk of death in critically ill patients.

INTRODUCTION: Decreased production of cathelicidin antimicrobial protein-18 (hCAP18) has been proposed to be a key mechanism linking decreased 25-hydroxyvitamin D (25D) levels with adverse outcomes among critically ill patients. However, few studies in humans have directly assessed plasma hCAP18 levels, and no study has evaluated the association between hCAP18 levels and adverse outcomes among critically ill patients. METHODS: We performed a single-center, prospective cohort study among 121 critically ill patients admitted to intensive care units (ICUs) between 2008 and 2012. We measured plasma hCAP18, 25D, D-binding protein, and parathyroid hormone levels on ICU day 1. The primary endpoint was 90-day mortality. Secondary endpoints included hospital mortality, sepsis, acute kidney injury, duration of mechanical ventilation, and hospital length of stay. RESULTS: ICU day 1 hCAP18 levels were directly correlated with 25D levels (Spearman's rho (rs) = 0.30, P = 0.001). In multivariate analyses adjusted for age and Acute Physiology and Chronic Health Evaluation II (APACHE II) score, patients with hCAP18 levels in the lowest compared to highest tertile on ICU day 1 had a 4.49 (1.08 to 18.67) greater odds of 90-day mortality, and also had greater odds of sepsis. ICU day 1 levels of other analytes were not associated with 90-day mortality. CONCLUSIONS: Lower 25D levels on ICU day 1 are associated with lower hCAP18 levels, which are in turn associated with a greater risk of 90-day mortality. These findings provide a potential mechanistic basis for the frequently observed association between low 25D levels and poor outcomes in critically ill patients.